The chemical name of Irbesartan is 2-Butyl-3-[[2′-(1H-tetrazol-5-yl)[1,1′-biphenyl]-4-yl]methyl]-1,3-diazaspiro[4,4]non-1-en-4-one and formula is C25H28N6O and molecular weight is 428.53. The current pharmaceutical product containing this drug is being sold by Sanofi Synthelabo using the tradename AVAPRO, in the form of tablets. Irbesartan is useful in the treatment of diabetic nefropathy, heart failure therapy and hypertension. Irbesartan is angiotension II type I (AII1)-receptor antagonist. Angiotension II is the principal pressor agent of the rennin-angiotension system and also stimulates aldosterone synthesis and secretion by adrenal cortex, cardiac contraction, renal resorption of sodium, activity of the sympathetic nervous system and smooth muscle cell growth. Irbesartan blocks the vasoconstrictor and aldosterone-secreting effects of angiotension II by selectively binding to the AT1 angiotension II receptor.
U.S. Pat. Nos. 5,270,317 and 5,559,233 describes a process for the preparation of N-substituted heterocyclic derivatives which involves reacting a heterocyclic compound of the formula
with a (biphenyl-4-yl)methyl derivative of the formula
wherein R1, R2, R3, R4, R5, and t, z and Hal have the meanings given in said U.S. Pat. No. 5,270,317, in the presence of an inert solvent such as DMF, DMSO or THF, with a basic reagent, for example KOH, a metal alcoholate, a metal hydride, calcium carbonate or triethylamine. The products of the reaction were purified by chromatography.
U.S. Pat. Nos. 5,352,788, and 5,559,233, and WO 91/14679 also describe identical alkylation of the nitrogen atom of the heterocyclic compound with the halo-biphenyl compound using the same inert solvent and the same basic reagents.
Also Canadian Patent No. 2050769 describes the alkylation of the nitrogen atom of the heterocycle of the formula
with a compound of the formula
wherein X, R1, Z1 and Z6 have the meanings given therein, in the presence of N,N-dimethylformamide and a basic reagent, such as alkali metal hydrides for example sodium or potassium hydride.
All of the above identified patents describe alkylation in solvents, such as N,N-dimethylformamide or DMSO, etc. in the presence of a basic reagent, for example, a metal hydride or a metal alcoholate etc. The strong bases, such as metal hydride or a metal alcoholate require anhydrous reaction conditions. Since N,N-dimethylformamide is used as a solvent, its removal requires high temperature concentration by distillation, which can result in degradation of the final product. The product intermediate is also purified by chromatography which is commercially not feasible and cumbersome on large scale.
Another process given in Canadian Patent No. 2050769 provides synthetic scheme as herein given below.

This process comprises the steps of protecting carboxylic group present on cyclopentane ring which is deprotected in consecutive step by vigourous hydrogenation condition in autoclave which is operationally difficult at a large scale.
US Patent No. 2004242894 also discloses the process of preparation of Irbesartan from 4-bromomethyl biphenyl 2′-(1H-tetrazol (2-triphenylmethyl) 5-yl) and Ethyl ester of 1-Valeramido cyclopentanecarboxylic acid in toluene in presence of base and PTC, and then hydrolyzing the protecting group. However this requires chromatographic purification.
This patent also discloses the process of preparation of tetrazolyl protected Irbesartan using 2,6 lutidine and oxalylchloride in toluene. However in this process the yield is as low as 30%.
US Patent No. 2004192713 discloses the process of preparation of Irbesartan by condensing the two intermediates via Suzuki coupling reaction. The reaction scheme is as given herein below.

However, this process has several disadvantages such as use of the reagents like butyl lithium and triisobutyl borate at low temp such as −20 to −30° C. under Argon atmosphere condition which is difficult to maintain at commercial scale.
WO2005113518 discloses the process of preparation of Irbesartan by condensing n-pentanoyl cycloleucine (V) with 2-(4-aminomethyl phenyl) benzonitrile (VI) using dicyclocarbodiimide (DCC) and 1-hydroxy benzotriazole as catalyst to give an open chain intermediate of formula (VIII) which is then cyclized in the presence of an acid, preferably trifluoro acetic acid to give cyano derivative of formula (VII) and which in turn is converted to Irbesartan by treating it with tributyl tin chloride and sodium azide.

In this application further describes another process comprising the steps of reacting 2-butyl-1,3-diazaspiro[4,4]non-1-en-4-one monohydrochloride (A) with 4-bromobenzyl bromide (B) in presence of base and solvent to give 3-[4-bromobenzyl]-2-butyl-1,3-diazaspiro[4,4]non-1-en-4-one (C) which is condensed with 2-[2′-(triphenylmethyl-2′H-tetrazol-5′-yl)phenyl boronic acid in the presence of tetrakis triphenyl phosphine palladium and base to give Irbesartan (I).
However these processes suffer with several disadvantages such as it uses trifluoroacetic acid for the cyclization step which is highly corrosive material. The process requires an additional step of activation by DCC. This step not only increases number of steps but also create problem in handling DCC at an industrial scale as it is highly prone to hazard which makes the process least preferred on a large scale production of Irbesartan. Further it uses phenyl boronic acid derivative and triphenyl phosphine complex which are harmful for the skin and eye tissue and also harmful for respiratory system. Tetrakis triphenyl phosphine palladium is also a costly material which increases overall cost for the production of Irbesartan. Moreover the yield is as low as 22%.
All the above patents/applications are incorporated herein as reference.
In summary, prior art relating to the process for the preparation of Irbesartan suffers with several drawbacks such as                i) It requires chromatographic purification of intermediates at various stages.        ii) It requires specific autoclave conditions for a deprotection of protecting group.        iii) It requires maintaining low temperature conditions such as −30° C. and requires special handling care and air and moisture tight condition with the reagents such as butyl lithium and triisobutyl borate.        iv) It uses hazardous and highly corrosive reagents.        v) It suffers low yield problem.        vi) All the process is having more number of reaction steps.        
It is therefore, a need to develop a process which not only overcomes the disadvantages of the prior art but also economical, operationally simple and industrially applicable. Present inventors have directed their research work towards developing a process for the preparation of Irbesartan which is devoid of the above disadvantages.